It is known to provide horizontal lifeline safety systems for workers on elevated structures.
Such fall protection systems commonly consist of a horizontal lifeline anchored at its ends to a building structure, including ceilings, walls and roof structures, and supported intermittently along its length by intermediate supports. Persons working in the vicinity of the lifeline may don a safety harness or belt and moveably attach to the horizontal lifeline via one or more mobile attachment devices. The mobile attachment devices freely move along the horizontal lifeline, including across the intermediate supports.
It is well known to include means for absorbing energy in such horizontal lifeline systems, so as to ensure that the maximum arrest forces exerted upon persons using such fall protection systems do not exceed physically injurious levels, and also to reduce the force placed on the anchorages therefor to manageable levels.
In modern fall protection systems, it is most common to utilize a substantially inelastic lifeline and to delegate energy absorption functionality to separate energy absorption apparatus that does not exhibit undesirable rebound.
Energy absorption apparatus interposed between a horizontal lifeline and its anchorage are most commonly termed “energy absorbers”, and energy absorption apparatus interposed between a lanyard and a harness are most commonly termed “shock absorbers” but the terms are used somewhat interchangeably in the art, and indeed; many types of energy absorption apparatus are used interchangeably (to wit, in both applications). Accordingly, such apparatus are hereinafter referred to universally as “energy absorbers” for simplicity.
U.S. Pat. No. 5,598,900 (O'Rourke), issued Feb. 4, 1997, exemplifies one class of energy absorber of the prior art. In this energy absorber, a pair of rings is provided, which are secured to one another by a strip of tear-ply webbing material and by a strip of woven webbing material.
In a fall, the tear-ply webbing separates incrementally, with consequent absorption of energy, until such time as the energy absorber elongates to the length of the woven webbing material, whereupon elongation stops, and further loading is borne by the woven webbing material.
This energy absorber is known to be relatively inexpensive to manufacture, and to provide satisfactory energy absorption, but, by virtue of its nature, is useful only for a single use, which is disadvantageous inter alia from the standpoint of economy.
U.S. Pat. No. 5,197,573 (De La Fuente et al.), issued Mar. 30, 1993, exemplifies another class of energy absorber.
This energy absorber, which is of all metal construction, and which dissipates kinetic energy in a fall by rolling balls which are forced by a tapered surface on an expandable sleeve to frictionally load a force rod, is suitable for repetitive use, and as such, overcomes some of the drawbacks of the class exemplified by the O'Rourke patent, but is of relatively complex and expensive construction.
US Patent Publication No. 20040145098 to Thaler, provides an energy absorber comprising a housing, a plunger and a compressible cushion. This energy absorber is suitable for repetitive use, and as such, overcomes some of the drawbacks of the class exemplified by the O'Rourke patent, but is of relatively more expensive construction.